Crystalline transformation from ta-C to graphene induced by a catalytic Ni layer during annealing

As an alternative strategy to fabricate high-performance graphene over a large area, metal catalysis has been attempted at elevated temperatures with various solid carbon sources such as polymers and amorphous carbon. Due to the diversity of amorphous carbon materials and the variety of metal catalysts used in the processes, the crystalline transformation from the amorphous carbon state to the graphene phase is not yet clearly understood. Here, we fabricated hydrogen free tetrahedral amorphous carbon (ta-C) as a solid carbon source, and nickel was chosen for the catalytic metal layer, which thereafter were integrated into a designed Si/SiO2/ta-C/Ni sandwich structure. The effect of thermal annealing in the range of 400 °C to 900 °C on the transformation of atomic carbon bonds was investigated. The results showed that the formation of the graphene phase emerged at an annealing temperature of 600 °C. Further increasing the temperature to 900 °C stimulated enhanced quality of graphene, but the quality was poor due to the oversaturated carbon content and the agglomeration of the Ni layer. Decreasing the thickness of ta-C to 2 nm led to graphene with 3–4 layers at a temperature of 800 °C, where metal-induced layer exchange was proposed as the key factor for the crystalline transformation from ta-C to graphene during thermal annealing. The results introduce a new strategy for the fabrication of high-quality graphene from tetrahedral amorphous carbon. [Display omitted] •The transformation and diffusion behaviors of ta-C are investigated in detail.•The metal-induced layer exchange mechanism is proposed for the growth of graphene.•High-quality, controllable graphene was grown at 800 °C.•The number of layers of graphene is dependent on the thickness of ta-C.